Processing of copper alloys

ABSTRACT

Phosphor-bronze, nickel-silver, beryllium-copper, and cupronickel alloys, when cold worked to an area reduction of at least 65 percent, and given a critical partial terminal anneal, exhibit higher yield strengths for given amounts of formability than have heretofore been attained.

United States Patent Chin et al. [4 May 16, 1972 54] PROCESSING OF COPPER ALLOYS 2,365,208 12/1944 Morris ..l48/11.5 72 Inventors: Gilbert Y. Chin, Murray 11111; Robert R. gfiggggg 3 32; 123;

Hart Plainfield both 6fN.1. l

3,046,166 7/1962 Hartmann ..148/11.5 R [73] Assignee: Bell Telephone Laboratories, Incorporated,

Berkeley Heights, N .J FOREIGN PATENTS OR APPLICATIONS 22 i May 21 19 9 486,600 6/1938 Great Britain ..148/ll.5 621,224 4/1949 Great Britain 148/ 12.7 1 P-p N04 826,468 1,032,441 6/1966 Great Britain ..148/1l.5

Related Application Data Primary ExaminerL. Dewayne Rutledge [63] Continuation-impart of Ser. No. 802,438, Feb. 26, A is ant EmminerW. W.Stal1ard 1969, abandoned. Attorney-R. J. Guenther and Edwin B. Cave [52] U.S. C1. ..l48/1l.5 R [57] ABSTRACT 5 Phosphor-bronze, nickel-silver, beryllium-copper, and cupro- "f nickel alloys, when cold worked to an area reduction of at least 65 percent, and given a critical partial terminal anneal, [56] Rem-mm Clted exhibit higher yield strengths for given amounts of formability UNITED STATES PATENTS than have heretofore been attained.

2,079,239 5/1937 Barthel ..148/] 1.5 6 Claims, 8 Drawing Figures I 1 120}- l 1 .01 YIELD 11o- STRENGTH l 90- 1 1 1 IN DIRECTION 701 OF ROLLING T 1 TRANSVERSE :60-

3o- 5 2o 65 5 10- g E 0 1 1 1 1 I 1 1 1 1 1 1 400 500 TEMPERATURE-DEG. F FOR 2 HOURS CROSS REFERENCES TO RELATED APPLICATIONS This is a continuation-in-part of the copending application,

Ser. No. 802,438, filed Feb. 26, 1969, now abandoned and relates to processing of copper alloys.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for processing of copper alloys to high yield strengths for given amounts of formability, and to the resulting product.

2. Description of the Prior Art Materials which are to be formed into springs, diaphragms, bellows, hose, wire connectors and other similar flexible articles desirably exhibit both a high degree of formability and the ability to sustain large applied loads and still return to their original configuration after unloading. The latter quality of resistance to permanent deformation is often designated as the yield strength, and is defined as the amount of loading stress required to produce a permanent set of a specified amount, usually 0.01 percent strain.

Commonly used in such applications are various copper alloys, such as the nickel silvers, the phosphor bronzes and the beryllium coppers. With the exception of the beryllium coppers, which are known to be precipitation hardenable by heat treating, increases in yield strengths of such materials are commonly achieved commercially by cold working them to varying degrees prior to final forming operations. Hence, the strength of such a material is usually classified by its temper," denoting the amount of cold working it has received. A strip material, for example, may have an anneal temper (no cold work), half hard temper (cold work equal to 21 percent reduction in thickness), hard temper 37 percent), extra hard temper (50 percent), spring temper (60 percent) or extraspring temper (69 percent). The increase in strength due to cold work, however, is usually accompanied by loss of formability, particularly at large reductions, so that the extent of cold work is limited by the severity of the subsequent forming operations. Cold working of phosphor bronze, for example, must often be limited to about 60 percent area reduction (spring temper) in order to preserve sufiicient formability for subsequent forming to springs. Increasing the amount of working so as to result in only about an additional 10 percent reduction leads to a loss of formability to the extent that many forming operations are rendered impossible.

It is generally known that formability may be recovered following cold working by subjecting the material to a terminal anneal. However, such anneals often result in a loss of the yield strength through recrystallization of the cold worked structure.

For example, a spring temper phosphor bronze strip which has been subjected to a terminal anneal following cold working may exhibit an increase in elongation of from about 3 percent to 56 percent, but a 0.01 yield strength decrease of from about 60,000 psi to 18,000 psi, which is too low for many applications. See Gohn et al., The Mechanical Properties of Wrought Phosphor Bronze Alloys," B.T.L. Monograph 2531, 1956.

SUMMARY OF THE INVENTION It has been discovered that cold working of certain copper alloys to area reductions of at least 65 percent, followed by a critical partial terminal anneal, results in these alloys having higher yield strengths for given amounts of formability than have heretofore been attained.

The metals so processed exhibit improved performance as springs, diaphragms, bellows, flexible hose and wire connectOlS.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph of 0.01 percent yield strength (psi X 10*) and minimum bending radius (64th of inch), each measured both transverse to and along the rolling direction, after a thickness reduction of a nickel silver alloy of 97.3 percent and a two hour terminal anneal, versus terminal anneal temperature (F.);

FIG. 2 is a graph similar in all respects to the graph of FIG. 1 except that the property reported is modulus of elasticity (psi X 10');

FIG. 3 is a graph similar in all respects to the graph of FIG. 1 except that the properties are reported for a phosphor bronze alloy;

FIG. 4 is a graph similar in all respects to the graph of FIG. 3 except that the property reported is modulus of elasticity (psi x 10');

FIG. 5 is a graph of 0.01 percent yield strength (psi X 10*) measured both transverse to and along the rolling direction, after a thickness reduction of a beryllium copper alloy of 96.5 percent and two hour terminal anneal, versus terminal anneal temperature (F.);

FIG. 6 is a graph similar in all respects to the graph of FIG. 5 except that the property reported is modulus of elasticity (psi X 10 FIG. 7 is a graph of 0.01 percent yield strength (psi X 10*) measured along the rolling direction, after a thickness reduction of a cupro-nickel alloy of 96.3 percent and a 2-hour terminal anneal, versus terminal anneal temperature (F.); and

FIG. 8 is a graph similar in all respects to the graph of FIG. 7 except that the property reported is modulus of elasticity (psi x 10').

DETAILED DESCRIPTION The process to be described applies to copper alloys containing at least 40.0 percent copper. Of particular interest, however, for their relatively high strengths and formabilities, particularly when treated by the inventive process, are: the phosphor bronzes, of nominal composition in weight percent 4.5 tin, 94.8 copper and 0.26 phosphorous, and typically having compositions in weight percent within the range 1.25 to 10 tin, to 99 copper, 0.03 to 0.35 phosphorous and up to 4 zinc and lead; the nickel silvers, of nominal composition in weight percent 12 nickel, 30 zinc and 58 copper, and typically having compositions in weight percent within the range of 9 to 33 nickel, 5 to 30 zinc and 53 to 75 copper; the beryllium coppers, of nominal composition in weight percent of 1.90 beryllium, 0.2 cobalt, balance copper, and typically having compositions in weight percent in the range of 0.4 to 2.05 beryllium, 0.2 to 0.6 cobalt, nickel, or iron, balance copper; and the cupro-nickels, of nominal composition in weight percent of 89 copper, 9 nickel, and 2 tin, and typically having compositions in weight percent in the range of 75 to 98 copper, 0.05 to 20 nickel, and 0 to 5 tin.

The essential steps of cold working followed by the partial terminal anneal may be preceded by any number of processing steps including one or more area reductions followed by one or more partial or dead anneals. However, it is stressed that the advantages of the inventive process may only be realized by concluding with cold working to an area reduction of at least 65 percent, followed by the final step of critically partially annealing the metal. Cold reduction may be accomplished by any of a number of methods, including rolling, swagging, extruding, and drawing. The percent area reduction due to cold working by rolling is defined for sheet and strip as working to a area reduction of at least 65 percent will ordinarily result in adequate levels of 0.01 yield strength and require the anneal step to recover needed formability. Such annealing may result in even further increases in the yield strength. Cold working to at least 95 percent area reduction is preferred for optimum results, since not only is the yield strength after such heavy reduction substantially increased over that obtainable for a 65 percent reduction, but also the partial terminal anneal generally results in an even larger further increase in yield strength and in an increase in modulus of elasticity (ratio of stress to strain within the elastic range) over the non-annealed state, as compared with the 65 percent reduced state.

Improvement in the modulus of elasticity is significant in the design of all flexible structures, particularly springs. For example, increases obtainable in modulus of elasticity by the inventive process may enable the use of less material to achieve a spring of comparable stiffness.

Thus, the main purpose of the critical partial terminal anneal is to recover at least some portion of the formability lost by cold working and needed for formation of the metal into springs, diaphragms, bellows, flexible hose, wire connectors and similar articles, while maintaining or even increasing the yield strength and modulus of elasticity.

The optimum anneal conditions will vary slightly among particular alloys and applications. However, it may be stated that in general annealing the metal at a temperature of from 100 F. to 1,000 F. for a time of from 20 hours to 1 second, the higher temperatures corresponding to shorter times, will result in some noticeable recovery of formability, with substantial preservation of yield strength. Exceeding these limits by an over-anneal will result in substantial loss of yield strength, while an insufficient anneal will not noticeably improve formability.

The following examples illustrate some optimum anneal conditions for some typical alloy compositions.

EXAMPLE 1 A 0.380 inch thick sheet of nickel silver alloy of composition in weight percent 12 nickel, 30 zinc and 58 copper, in annealed temper, was subjected to a series of processing steps ending in cold rolling to a thickness of 0.010 inch, corresponding to an area reduction of 97.3 percent. It was then formed into standard tensile specimens with the tensile axis either parallel to or transverse to the rolling direction. The specimens were divided into sets, and each set was annealed at a different temperature for two hours. Samples from each set were then tested in tension for 0.01 yield strength, (psi X) and modulus of elasticity (psi X 10'), on an Instron machine at a strain rate of about 0.050 inch per inch per minute.

Minimum bending radius in 64th inches was obtained as a measure of formability by bending test strips to 90 angles around bending shoes of successively smaller radii until such bending resulted in failure of the strips. It has been observed that for the copper alloys of interest, a minimum bending radius of six sixty-fourths inch for an alloy thickness of 0.01 inch is required for many forming operations, and is generally obtainable for the alloys of interest in spring temper. This radius will therefore be assumed to be a reasonably acceptable minimum value when presenting the data obtained; it is pointed out however, that formability is not a significant factor in some applications, and that in these cases materials having the highest yield strengths obtainable by the inventive technique may be used.

Since the required degree of reduction ordinarily results in a marked anisotropy in observed properties of sheets and strips of the alloys of interest, all properties are reported whenever possible both transverse to and in the direction of rolling, to aid the practitioner. Results for Example 1 are shown in FIGS. 1 and 2. In FIG. 1, as may be seen, as the anneal temperature is increased from about 75 F. to about 700 F., the yield strengths increase from about 65,000 psi for the non-annealed state, to about 100,000 psi at 500 F. in the rolling direction, and to about l20,000 psi at about 550 F. in the transverse direction, and decrease to about 65,000 psi at about 675 F. The minimum bending radius increases (formability decreases) from about four sixty-fourths inch to about nine sixty-fourths inch at about 400 F., and then decreases to about less than one sixty-fourth inch at about 675 F. In the transverse direction, the bending radius decreases rapidly from below twelve sixty-fourths inch to about two sixtyfourths inch at about 675 F.

It is thus seen that for a 2-hour anneal at a temperature of 650 F., the formability has been increased to six sixty-fourths inch in the transverse direction and to about one sixty-fourth inch in the rolling direction, while the increased yield strength obtained by cold working has been substantially retained. For smaller formability increases, further increases in yield strength are obtained by annealing at a temperature lower than 650 F. For example, for an anneal temperature of about 600 F a bending radius of about four sixty-fourths inch is obtained in the rolling direction, while the yield strength obtained is from 75,000 to 85,000 psi, and for applications where formability is not a factor, a maximum yield strength of 100,000 psi in the rolling direction is obtained at 500 F., and 120,000 psi in the transverse direction at 550 F. The latter value represents an increase of about percent over that obtainable by other than the inventive technique.

Referring now to FIG. 2, it is seen that some increases in modulus of elasticity have been obtained at a temperature of about 575 F., and are retained to at least 600 F., transverse to the rolling direction, and to at least 700 F. in the rolling direction. Thus, by the inventive process, substantial increases in both yield strength and modulus of elasticity are obtainable, while the formability is at least partially recovered, and in some cases improved over the non-annealed state EXAMPLE 2 The procedure of Example 1 was followed for phosphor bronze A-l alloy having a composition range in weight percent from 4.2 to 5.8 tin, 0.03 to 0.35 phosphorous, up to 0.3 zinc, balance copper. Results are shown graphically in FIGS. 3 and 4. In FIG. 3 it is seen that the shapes of the curves are similar to those of FIG. 1 for nickel silver. It is seen that the yield strength in the rolling direction increases from about 88,000 psi to about 105,000 psi at about 225 F, and decreases to 80,000 psi, about the value achieved by cold working, at about 475 F. The transverse 0.0] percent yield strength increases from about 93,000 psi to about 110,000 psi at about 350 F. and has fallen to about 100,000 psi at 525 F well above the value achieved by cold working alone. The bending radius in the rolling direction decreases gradually from about six sixty-fourths inch to less one sixty fourth inch at about 550 F., while the transverse bending radius decreases rapidly above the 375 F. to less than one sixty-fourth inch at about 550 F. In FIG. 4, it is seen that the modulus of elasticity rises gradually to a peak at about 510 F., and then falls off. It is thus seen that for an anneal at about 500 F., a minimum amount of formability has been achieved, while increases in the modulus of elasticity and transverse yield strength over the non-annealed state have also been achieved. About 500 F., substantial increases in formability may be achieved without significant loss of the 0.01 yield strength achieved by cold working. In the rolling direction, minimum formability is met at all annealing temperatures, with substantially higher yield strengths than heretofore obtained.

Thus, by the inventive process, substantial increases in both modulus of elasticity and yield strength are obtainable for phosphor bronze, while the formability is at least partially recovered and in some cases improved over the non-annealed state.

EXAMPLE 3 A 0.288 inch thick sheet of beryllium copper of composition in weight per cent 1.95 beryllium, remainder copper, in spring temper was subjected to a series of processing steps ending in cold rolling to a thickness of 0.010 inch, corresponding to an area reduction of 97.3 percent. The procedure of Example 1 was then followed to obtain 0.01 yield strength and modulus of elasticity. Results are shown graphically in FIGS. 5 and 6, in which it is seen that the shapes of the yield strength and modulus curves are similar to those of the previous figures. It is seen from FIG. 5 that the yield strength in the rolling direction increases from about 80,000 psi, the value achieved by cold working, to about 145,000 psi at about 525 F and decreases to about 100,000 psi at about 700 F. The transverse yield strength increases from about 100,000 psi to about 170,000 psi at about 525 F. This latter value represents an increase of about percent cent over that obtainable by other than the inventive technique. In addition, the annealing temperature to achieve peak strength (525 F.) is about 100 F. lower than the prior art treatment. This may be advantageous in terms of power savings and in annealing a heat sensitive assembled structure containing beryllium copper components. The yield strength then decreases to about 120,000 psi at about 700 F. In FIG. 6, it is seen that the modules of elasticity rises gradually, except for an abrupt increase at about 525 F. Since the beryllium coppers are often used in applications not requiring a high degree of formability, the anneal conditions may be chosen with regard to optimizing the yield strength and modulus of elasticity values, without regard to formability. For example, at an anneal of 525 F. for two hours, substantial increases in modulus of elasticity and maximum increases in 0.01 yield strength have been obtained. EXAMPLE 4 A 0.188 inch thick sheet of cupro-nickel of composition in weight per cent 89 copper, 9 nickel, and 2 tin, in spring temper, was subject to a cold reduction of 96.3 per cent and a thickness of 0.006 inch. The procedure of Example 1 was then followed to obtain 0.01 yield strength and modulus of elasticity. Results are shown in FIGS. 7 and 8, in which it is again seen that the shapes of the curves are similar to those of the previous figures. In FIG. 7 it is seen that yield strength increases gradually from a cold worked value of about 60,000 psi to about 75 ,000 psi at about 500 F then increases rapidly to a maximum value of 88,000 psi at about 625 F. This value represents an increase of about 75 per cent over values obtainable by other than the inventive method. After the 2 hour anneal at this temperature, minimum bending radius is about two sixty-fourths inch in the direction of rolling and one sixtyfourth inch transverse to the rolling direction, indicating acceptable formability. In FIG. 8 it is seen that modulus of elasticity increases gradually from about 300 F. to a maximum at about 600 F.

It is thus seen that, for the cupro-nickel alloys, substantial increases in both modulus of elasticity and 0.01 percent yield strength are obtained while needed formability is recovered by inventive technique. Furthermore, the optimum increases in yield strength and modulus of elasticity coincide for partial terminal anneals within the range of about 600 F. to 700 F. for two hours, for which acceptable formability is achieved. Tests indicate that even greater increases in strength properties are obtainable in the direction transverse to rolling for the cupro-nickel alloys.

What is claimed is:

l. A method for processing copper alloys selected from the group consisting of beryllium, copper, phosphor-bronze and cupro-nickel alloys comprising one or more processing steps, characterized in that said steps conclude with: cold working the alloys to an area reduction of at least 65 per cent, said cold working consisting of one or more cold reduction steps, followed by a partial terminal anneal at a temperature of from 100 F. to 1,000 E, for a time of from 20 hours to 1 second, the higher temperatures corresponding to shorter times.

2. The method of claim 1 in which the cold working is carried out to an area reduction of at least per cent.

3. The method of claim 1 in which the copper alloy comprises in weight per cent 0.5 to 2.05 beryllium, remainder c er.

3 A method for processing copper alloys selected from the group consisting of nickel silver alloys comprising one or more processing steps, characterized in that said steps conclude with: cold working the alloys to an area reduction of at least 95 per cent, said cold working consisting of one or more cold reduction steps, followed by a partial terminal anneal at a temperature of from to 1,000 F for a time of from 20 hours to 1 second, the higher temperatures corresponding to shorter times.

5. The method of claim 4 in which the copper alloy comprises in weight per cent 9 to 33 nickel, 5 to 30 zinc and 53 to 75 copper.

6. The method of claim 5 in which the copper alloy is annealed at a temperature of from about 225 to about 700 F. for about 2 hours.

UNITED STATES PATENT OFFICE (IERTIFICATE 0F CORRECTION Patent 2.66%. Q11 Dated Mav 16. 1972 Inventor(s) Gilbert Y. Chin; Robert R. Hart It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

n n Column 2, line 70, change I to t Column l, line 3%, after "state" insert for nickel silver.,'

line 59, change About" to Above-.

Column 5, line 13, after "percent" delete "cent" Column 6, line 28, change "0.5" to O.

Signed and sealed this ll th day of November 1972.

(SEAL) I I 1 Attest: 1 EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents )RM PO-1050(\0-69) USCOMM-DC 60370-P69 6 II.S.GOVIINNIN1 PIIIR'ING nInCI "I! 0-3IO-UI 

2. The method of claim 1 in which the cold working is carried out to an area reduction of at least 95 per cent.
 3. The method of claim 1 in which the copper alloy comprises in weight per cent 0.5 to 2.05 beryllium, remainder copper.
 4. A method for processing copper alloys selected from the group consisting of nickel silver alloys comprising one or more processing steps, characterized in that said steps conclude with: cold working the alloys to an area reduction of at least 95 per cent, said cold working consisting of one or more cold reduction steps, followed by a partial terminal anneal at a temperature of from 100* to 1,000* F., for a time of from 20 hours to 1 second, the higher temperatures corresponding to shorter times.
 5. The method of claim 4 in which the copper alloy comprises in weight per cent 9 to 33 nickel, 5 to 30 zinc and 53 to 75 copper.
 6. The method of claim 5 in which the copper alloy is annealed at a temperature of from about 225* to about 700* F. for about 2 hours. 